In any particular area, the cost will be approximately linear. If all you’re looking at is the emissions in one state caused by one group of things (like power plants) over the course of one year, then it’s approximately linear. Also, depending on how accurately you can guess at what the market equilibrium will be, you can narrow it down further so the linear approximation is still more accurate.
That doesn’t seem to be a reasonable assumption at all—expected damage seems to escalate faster at the extreme end.
In any particular area, the cost will be approximately linear. If all you’re looking at is the emissions in one state caused by one group of things (like power plants) over the course of one year, then it’s approximately linear. Also, depending on how accurately you can guess at what the market equilibrium will be, you can narrow it down further so the linear approximation is still more accurate.